Electrical connection contact for a ceramic component, a ceramic component, and a component arrangement

ABSTRACT

An electrical connection contact (5) for a ceramic component (2) is specified. The connection contact (5) comprises a first material (M1) and a second material (M2) arranged thereon, wherein the first material (M1) has a high electrical conductivity and the second material (M2) has a low coefficient of thermal expansion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage of International ApplicationNo. PCT/EP2016/054007, filed Feb. 25, 2016, which claims the benefit ofGermany Patent Application No. 10 2015 102 866.2, filed on Feb. 27,2015, both of which are incorporated herein by reference in theirentireties.

A connection contact for a ceramic component is specified. Theconnection contact is formed from a metal sheet, for example. Inparticular, the connection contact can be embodied as a lead frame orconnection bracket.

Ceramic components require an electrical contacting for interconnectionin electronic systems, e.g. by means of a printed circuit board.External contacts of the ceramic component are typically connected tothe contact locations of a printed circuit board by a solder material.In power electronics, a particular technical challenge consists inrealizing a thermomechanically stable linking that simultaneously offersthe best possible electrical and thermal conductivity and a goodradio-frequency behavior.

DE 10 2013 108 753 A1 describes a ceramic component comprising aconnection element.

It is an object of the present invention to specify an improvedconnection contact for a ceramic component.

In accordance with a first aspect of the present invention, anelectrical connection contact for a ceramic component is specified. Theconnection contact preferably serves for the electrical connection ofthe component on a carrier. By way of example, the connection contactserves for feeding electrical voltage and electrical signals to thecomponent. Furthermore, the connection contact can also serve forproducing a mechanical securing and, if appropriate, a thermalconnection to the carrier.

The ceramic component is preferably embodied as a multilayer component.By way of example, the component comprises a main body with ceramiclayers and electrode layers arranged one above another. The layers arepreferably sintered jointly. In particular, a capacitor, preferably apower capacitor, can be involved.

The connection contact is designed for securing on the component.Preferably, the connection contact is formed from a metal sheet. In thiscase, from a planar metal sheet, for example, firstly a planar piecehaving the dimensions of the connection contact is formed, for exampleby stamping out. Afterward, the connection contact is preferably broughtto a bent shape. By way of example, the connection contact has an angledshape. The connection contact can also be a lead frame.

By way of example, the connection contact comprises at least one contactregion for securing the connection contact on a main body of the ceramiccomponent. Furthermore, the connection contact comprises for example atleast one connection region for securing on a carrier, in particular ona printed circuit board. The connection region is preferably arranged atan angle with respect to the contact region. By way of example, theconnection region is bent outward or inward.

In one embodiment, the connection contact comprises two connectionelements. The connection elements are preferably designed for securingon opposite sides of the main body. The properties of the connectioncontact preferably correspondingly apply to each individual connectionelement.

The connection contact preferably comprises a material composite. Inthis case, the materials are arranged one above another in the form oflayers, for example. In one embodiment, the connection contact comprisesa first material and a second material arranged thereon. The firstmaterial is preferably embodied as a first layer and the second materialas a second layer.

The first material has a high electrical conductivity. A high electricalconductivity is for example at least m/(Ω·mm²), preferably at least 50m/(Ω·mm²). Preferably, the first material also has a high thermalconductivity. A high thermal conductivity is for example at least 250W/(m·K), preferably at least 350 W/(m·K).

The second material preferably has particularly good mechanical andthermomechanical properties. In particular, the second material has alow coefficient of thermal expansion. A low coefficient of thermalexpansion is for example at most 5 ppm/K, preferably at most 2.5 ppm/K.The coefficient of expansion is preferably as close as possible to thecoefficient of expansion of the ceramic. A good thermal adaptation tothe ceramic can be achieved in this way. As a result, a build-up ofstress during temperature changes can be avoided for the most part andcracking in the component can largely be prevented.

In one preferred embodiment, the first material comprises copper orconsists of copper. Copper has a particularly good electrical andthermal conductivity. By way of example, the second material comprisesan iron-containing alloy. Preferably, the second material comprisesInvar or consists of Invar. Invar denotes an iron-nickel alloycomprising approximately ⅓ nickel and ⅔ iron. This material has aparticularly low coefficient of thermal expansion. In particular, thecoefficient of thermal expansion is close to the coefficient ofexpansion of the ceramic. On account of the combination with the firstmaterial, even when the second material has a low electricalconductivity it is possible to ensure a sufficient conductivity for theconnection contact.

In one embodiment, the connection contact additionally comprises a thirdmaterial. The third material is arranged on the second material, suchthat the second material is arranged between the first material and thethird material. The third material is preferably embodied as a thirdlayer. Preferably, the third material is identical to the firstmaterial. Preferably, the third layer has the same thickness as thefirst layer. The embodiment of the third material makes it possiblepreferably to prevent warpage of the connection contact in the event ofa temperature change.

In particular, the connection contact can comprise a material compositecomposed of copper-Invar-copper. Such a composite can also be referredto as CIC composite.

In accordance with a further aspect of the present invention, a ceramiccomponent comprising an electrical connection contact is specified. Theconnection contact and the ceramic component can be embodied asdescribed above. In particular, the connection contact is secured on amain body of the component. The ceramic component is a ceramicmultilayer capacitor, for example.

The connection contact is preferably secured on a main body of thecomponent. By way of example, the connection contact comprises twocontact elements arranged on opposite sides of the main body. The mainbody comprises an external contact, for example, on which the connectioncontact is secured. The external contact is embodied for example as ametal layer, in particular as a sputtered metal layer.

In one embodiment, the connection contact is secured on the main body bya contact material. The contact material is for example a sinteringmaterial, in particular sintering silver. In order to secure theconnection contact on the main body, the contact material is applied forexample on the main body and/or the connection contact. Afterward, theconnection contact is arranged on the main body and the contact materialis sintered. In this way, it is possible to obtain ahigh-temperature-resistant and low-impedance connection between the mainbody and the connection contact.

In one embodiment, the component is embodied in such a way that upon theconnection contact being secured on the carrier, the main body is spacedapart from the carrier. A thermal and mechanical decoupling of the mainbody from the carrier can be achieved in this way. By way of example,the main body is arranged in a non-centered manner at the connectioncontact in the height direction in such a way that an air gap is formedwith respect to a carrier.

In accordance with a further aspect of the present invention, acomponent arrangement comprising a ceramic component and a carrier, onwhich the component is secured, is specified. The component ispreferably embodied as described above and comprises in particular theconnection contact. The carrier is embodied for example as a printedcircuit board. A ceramic carrier can also be involved.

The connection contact is connected to the carrier by a connectingmaterial, for example. The connecting material is a solder material orsintering material, for example. In particular, the connection contactcan be connected to the carrier by the sintering of a sinteringmaterial. By way of example, the sintering is effected in a pressuresintering method or a pressureless sintering method.

In accordance with a further aspect of the present invention, a methodfor producing a connection contact for a ceramic component is specified.The connection contact is preferably embodied as described above.

During the production of the connection contact, a metal sheetcomprising the second material is provided. The second materialpreferably comprises Invar or consists of Invar. The first material isthen applied, for example rolled, onto the second material. The secondmaterial preferably comprises copper or consists of copper. Afterward,the third material can be applied, in particular rolled, onto theopposite side of the metal sheet. The third material is preferablyidentical to the first material.

The connection contact can then be brought to a desired shape. By way ofexample, the outer dimensions of the connection contact are defined in astamping process. The stamped-out piece is subsequently bent to adesired shape. In particular, an angled shape of the connection contactcan be formed as a result.

In accordance with a further aspect of the present invention, a methodfor producing a ceramic component comprising a connection contact isdescribed. In this case, a connection contact and a main body of thecomponent are provided. The main body and the connection contact arepreferably embodied as described above. The connection contact issubsequently secured on the main body. To that end, by way of example, acontact material is applied on the main body and/or the connectioncontact. In particular, the contact material is embodied as sinteringmaterial. Afterward, the connection contact is arranged on the main bodyand a sintering method is carried out.

A plurality of aspects of an invention are described in the presentdisclosure. All properties disclosed with respect to the connectioncontact, the component, the component arrangement and/or one of themethods are also correspondingly disclosed with respect to therespective other aspects, and vice versa, even if the respectiveproperty is not explicitly mentioned in the context of the respectiveaspect.

The subjects described here are explained in greater detail below on thebasis of schematic exemplary embodiments which are not true to scale.

In the figures:

FIG. 1A shows one embodiment of a component arrangement in a schematicsection view,

FIGS. 1B and 1C show detail views of the component arrangement from FIG.1A,

FIGS. 2 to 5 show various embodiments of components in perspectiveviews.

Preferably, in the following figures, identical reference signs refer tofunctionally or structurally corresponding parts of the variousembodiments.

FIG. 1A shows a component arrangement 1 comprising an electricalcomponent 2 and a carrier 3, on which the component 2 is arranged.

The electrical component 2 comprises a main body 4. The main body 4preferably comprises a ceramic material. In this case, the component 2is referred to as a ceramic component. The component 2 is embodied forexample as a multilayer component. In particular, the main body 4 cancomprise a layer stack having ceramic layers and electrode layersarranged therebetween. All the layers are preferably sintered jointly.By way of example, the electrode layers comprise copper. By way ofexample, the component 2 is embodied as a capacitor, in particular as aceramic multilayer capacitor. In particular, a power capacitor can beinvolved.

The component 2 comprises a connection contact 5 for the electricalconnection of the component 2. By way of example, the connection contact5 comprises two connection elements 18, 19. The connection elements 18,19 are arranged for example on opposite sides of the main body 4. It isalso possible for only one of the connection elements 18, 19 to bedesignated as connection contact 5.

The connection contact 5 electrically connects the component 2 to thecarrier 3. Furthermore, the connection contact 5 can also serve formechanically securing the component 2 on the carrier 3. The connectioncontact 5 can also ensure a thermal linking to the carrier 3.

The connection contact 5 is preferably produced separately from the mainbody 5 and subsequently secured on the main body 4. Preferably, theconnection contact 5 is formed from a metal sheet. In particular, theconnection contact 5 can be a connection bracket or leadframe. Theconnection contact 5 preferably has the lowest possible coefficient ofthermal expansion alongside a high thermal and electrical conductivity.These different properties are preferably ensured by a materialcomposite, in particular by a multi-layered construction of theconnection contact 5. The construction of the connection contact 5 isdescribed in detail in association with FIG. 1B.

The connection contact 5 comprises a contact region 6 for securing onthe main body 4 and a connection region 7 for securing on the carrier 3.The contact region 6 is secured on the main body 4 by means of a contactmaterial 8, for example. By way of example, the contact material 8 isarranged in layer form. By way of example, the contact material 8 is asintering material. The connection contact 5 is preferably secured onthe main body 4 by the sintering of the sintering material 8. By way ofexample, a low-temperature sintering process, in particular at atemperature in the region of 250° C., is carried out here.

The connection region 7 is arranged at an angle with respect to thecontact region 6. By way of example, the connection region 7 is orientedat an angle of 90° C. with respect to the contact region 6. Theconnection region can be bent outward or inward. In the case of aconnection region 7 bent inward, the connection region 7 preferably liesbelow the main body 4. In the case of a connection region 7 bentoutward, the connection region 7 preferably lies alongside the main body4. The connection contact 5 is preferably embodied in such a way thatthe main body 4 is arranged at a distance from the carrier 3. Inparticular, an air gap 9 is situated between the main body 4 and thecarrier 3.

The carrier 3 is a printed circuit board, for example. By way ofexample, the printed circuit board is embodied as an FR4 circuit board.A ceramic substrate can also be involved. By way of example, the carrier3 is embodied as a DCB (direct copper bonded) substrate in which copperis applied on a ceramic.

The carrier 3 has at least one contact location 10 on which theconnection region 7 of the connection contact 5 is secured. By way ofexample, the contact location 10 is a soldering pad or a copper contact.By way of example, the connection region 7 is soldered or sintered tothe contact location 10. To that end, by way of example, a connectingmaterial 11 in the form of a solder material or sintering material isprovided.

FIG. 1B shows an enlarged excerpt from FIG. 1A, the position of which isdepicted by “1B” in FIG. 1A. In particular, the multi-layeredconstruction of the connection contact 5 can be seen. The connectioncontact 5 comprises at least a first material M1 and a second materialM2 arranged thereon. The first material M1 differs from the secondmaterial M2. In particular, the materials M1, M2 are embodied as a firstlayer 12 and a second layer 13 arranged thereon. The first layer isarranged nearer to the main body 4 than the second layer 13.

The first material M1 and thus the first layer 12 preferably has aparticularly good electrical and thermal conductivity. The first layer12 comprises the first material M1 or consists of the first material M1.Preferably, the first material M1 is copper. Copper has a specificelectrical conductivity of approximately 58 m/(Ω·mm²), a thermalconductivity of approximately 400 W/(m·K) and a coefficient of thermalexpansion of approximately 18 ppm/K.

The second material M2 and thus the second layer 13 preferably has a lowcoefficient of thermal expansion. Furthermore, the second layer 13ensures for example the mechanical strength of the connection contact 5.The second layer 13 comprises the second material M2 or consists of thesecond material M2. By way of example, Invar is involved in this case.Invar has a specific electrical conductivity of approximately 1.2m/(Ω·mm²), a thermal conductivity of approximately 13 W/(m·K) and acoefficient of thermal expansion of <2 ppm/K.

Consequently, the first material M1 haws a significantly greaterelectrical and thermal conductivity than the second material M2. Thesecond material M2 has a significantly lower coefficient of thermalexpansion than the first material M1.

The connection contact 5 can additionally comprise a third material M3.The third material M3 can be the same material as the first material M1.The third material M3 forms a third layer 14, wherein the third layer 14is arranged on the second layer 13. The second layer 13 is arrangedbetween the first layer 12 and the third layer 14. Preferably, the thirdlayer 14 has the same thickness as the first layer 12. A bimetallicbehavior of the connection contact 5 can be prevented by the third layer14.

By way of example, the connection contact 5 has a thickness in the rangeof between 0.1 mm and 1 mm. In particular, the thickness can be 0.15 mm.By way of example, the ratio of the thickness of the second layer 13 tothe thickness of the first layer 12 is from 1:1 to 5:1. In particular,the ratio of the thicknesses is 3:1. In the case of an embodiment of athird layer 14, the ratio of the thickness of the third layer 14 to thethickness of the second layer 13 to the thickness of the first layer 12is for example from 1:1:1 to 1:5:1. In particular the ratio of thethicknesses is 1:3:1. By way of example, the second layer 13 comprisesInvar having a thickness of 90 μm, the first layer 12 comprises copperhaving a thickness of 30 μm and the third layer 14 comprises copperhaving a thickness of 30 μm. The coefficient of thermal expansion ofsuch a CIC connection contact is in the range of approximately 5-7ppm/K, for example, depending on the thickness ratio chosen.

The connection contact 5 can furthermore comprise one or a plurality offurther layers 15, 16. The further layers 15, 16 form for example theouter sides of the connection contact 5. By way of example,electroplating layers 15, 16, in particular silver layers, are involved.The electroplating layers have for example in each case a thickness inthe range of 5 μm to 10 μm. The further layers serve for example forpassivation for the first and/or the third layer 12, 14. In particular,these layers can offer tarnishing protection. Furthermore, these layerscan provide solderable surfaces or improve the connection to a sinteringmaterial.

In order to produce the connection contact 5, by way of example, thesecond layer 13 is provided and this is followed by arranging thereonthe first layer 12 and, if appropriate, the third layer 14. The secondlayer 13 is provided in particular as a metal sheet. By way of example,the first and third layers 12, 14, are rolled onto the second layer 13.Afterward, by way of example, the electroplating layers 15, 16 areapplied on both sides. By way of example, a piece is then stamped outfrom the multi-layered metal sheet and bent to a desired shape.

The connection contact 5 is preferably secured on an external contact 17of the main body 4. The external contact 17 is in electrical contactwith the electrode layers of the main body 4. The external contact 17comprises at least one sputtered layer, for example. The externalcontact 17 can comprise a plurality of layers arranged one aboveanother, in particular a plurality of sputtered layers. By way ofexample, the external contact 17 comprises components for adhesionpromotion, for a diffusion barrier and for further contacting. In oneembodiment, a Cr/Ni/AG layer construction is involved. By way ofexample, the external contact 17 has a thickness in the region of 1 μm.

The connection contact 5 is connected to the external contact 17 by acontact material 8. The contact material 8 preferably has a highelectrical and thermal conductivity. Furthermore, the contact material 8preferably has a high robustness vis-à-vis thermal cycling loads and ahigh adhesion force. By way of example, the contact material 8 comprisesa sintering material, in particular sintering silver. The connectioncontact 5 is then secured with the main body 4 by the sintering of thecontact material 8. By way of example, the contact material 8 has athickness in the region of 20 μm. The contact material 8 is embodied forexample like the contact layer described in DE 10 2013 108 753 A1.

In order to secure the connection contact 5 on the main body 4, by wayof example, the contact material 8 is applied on the main body 4 and/orthe connection contact 5. The connection contact 5, in particular theconnection elements 18, 19 are then arranged on the main body 4 andsecured in a sintering method. By way of example, a low-temperaturesintering method is carried out here as well.

FIG. 1C shows an enlarged excerpt from FIG. 1A, the position of which isdepicted by “1C” in FIG. 1A. In particular, the connection of theconnection contact 5 to a contact location 10 of the carrier 3 can beseen here. The carrier 3 with the contact location 10 is embodied forexample as a printed circuit board having contact pads or as a ceramicsubstrate having contact pads, in particular as a DCB substrate.

In one embodiment, the securing is realized by soldering. By way ofexample, for this purpose a lead-free SAC solder is used as connectingmaterial 11. In an alternative embodiment, the securing is realized bysintering. By way of example, for this purpose a sintering silvermaterial is used as connecting material 11. In this case, pressurelesssintering or pressure sintering can be carried out. In this case, theconnection regions 7 bent outward enable a particularly good connectionin a pressure sintering process, since pressure can be exerted directlyon the connection regions 7, without any risk of prior damage to themain body 4 or the external contact 17.

The construction of the connection contact 5 in its connection region 7corresponds to the construction in its contact region 6. In particular,the connection contact 5 comprises a multi-layered construction, forexample a CIC construction with electroplating layers applied on bothsides.

FIGS. 2 to 5 show various embodiments of connection contacts 5 andcomponents 2 comprising the connection contacts 5. The connectioncontacts 5 in each case comprise the material composite described withregard to FIGS. 1A-1C. All the components 2 can be secured on a carrierusing SMD mounting, i.e. surface mounting.

FIG. 2 shows a connection contact 5 in the same embodiment as theconnection contact 5 from FIGS. 1A-1C.

In particular, the connection contact 5 comprises two connectionelements 18, 19, which are arranged on opposite sides of a main body 4of a component 2. The connection elements 18, 19 each comprise a contactregion 6 and a connection region 7 bent outward. Consequently, theconnection region 7 leads away from the main body 4. In the case of sucha geometry, the connection contact 5 can be secured on a carrier 3particularly well in a pressure sintering process.

The main body 4 has a cuboidal shape. The connection contact 5 extendscompletely over two longitudinal sides of the main body 4. Theconnection contact 5 can also extend only partly over outer sides of themain body. There is a significant height difference between an undersideof the main body 4 and an underside of the connection region 7, suchthat the main body 4 can be arranged at a distance from the carrier 3.

FIG. 3 shows a further embodiment of a connection contact 5 and of acomponent 2 comprising the connection contact 5. In contrast to theconnection contact 5 from FIG. 2, the connection region 7 here is bentinward. The connection region 7 is arranged below the main body 4. Here,too, an air gap 9 is situated between an underside of the main body 4and an underside of the connection region 7. The main body 4 is thusarranged in a non-centered manner with respect to the connection contact5 in the height direction.

FIG. 4 shows a further embodiment of a connection contact 5 and of acomponent 2 comprising the connection contact 5. The component 2comprises a main body 4 having a plurality of partial bodies 20. By wayof example, five partial bodies 20 are provided. The connection contact5 comprises two connection elements 18, 19. A common electrical contactfor all the partial bodies 20 is produced via the connection contact 5.Consequently, the partial bodies 20 are connected in parallel.

The connection elements 18, 19 each comprise a plurality of connectionregions 7 for securing on a carrier. This enables stable securing evenin the case of a relatively large design. The connection regions 7 arebent outward.

Cutouts 21 are provided in the contact region 6. The contact region 6extends over an entire longitudinal side of the main body 4.

FIG. 5 shows a further embodiment of a connection contact 5 and of acomponent 2 comprising the connection contact 5. As in FIG. 4, thecomponent 2 comprises a main body 4 having a plurality of partial bodies20.

The component 2 is embodied in the form of a variable “endless” design.In particular, the component 2 can comprise as many partial bodies 20 asdesired and can subsequently be separated into smaller components 2. Tothat end, the connection contact 5 has a separable form, for example. Inparticular, the connection contact 5 comprises a multiplicity of partialconnections 22 that respectively contact a partial body 20. Each partialconnection 22 comprises a contact region 6 for contacting a partialbody. The contact regions 6 each comprise two contact arms that bear ona partial body 20. The connection contacts 5 are embodied in a resilientfashion, for example. The partial connections 22 can be connected to oneanother by thin webs (not shown). The partial connections 22 can besingulated by the webs being perforated.

In order to increase the mechanical stability, the component 2 comprisesa base 23, for example a plastic base, on which the main body 4 isarranged. The connection contact 5 is lead through the base 23.Alternatively, the connection contact 5 can also be lead around a narrowside of the base 23.

LIST OF REFERENCE SIGNS

-   1 Component arrangement-   2 Component-   3 Carrier-   4 Main body-   5 Connection contact-   6 Contact region-   7 Connection region-   8 Contact material-   9 Air gap-   10 Contact location-   11 Connecting material-   12 First layer-   13 Second layer-   14 Third layer-   15 Further layer-   16 Further layer-   17 External contact-   18 Connection element-   19 Connection element-   20 Partial body-   21 Cutout-   22 Partial connection-   23 Base-   M1 First material-   M2 Second material-   M3 Third material

The invention claimed is:
 1. A component, comprising a main body havingceramic layers and electrode layers and comprising an electricalconnection contact, the electrical connection contact comprising a firstlayer comprising a first material and a second layer comprising a secondmaterial arranged thereon, wherein the first material has a highelectrical conductivity and the second material has a low coefficient ofthermal expansion, wherein the electrical conductivity of the firstmaterial is at least 40 m/Ω mm² and the coefficient of thermal expansionof the second material is at most 5 ppm/K, wherein a relation of thethickness of the second layer to the thickness of the first layer is 1:1up to 5:1, wherein the electrical connection contact is secured on themain body by a contact material, wherein the contact material is asintering material, and wherein the thermal coefficient of the secondmaterial is at most 2.5 ppm/K and the thermal coefficient of theconnection contact as a whole is between 5 and 7 ppm/K.
 2. The componentaccording to claim 1, wherein the first material comprises copper andthe second material comprises Invar.
 3. The component according to claim1, which is formed from a metal sheet.
 4. The component according toclaim 1, comprising a third material arranged on the second material,wherein the second material is arranged between the first material andthe third material.
 5. The component according to claim 4, wherein thematerials are arranged one above another as first, second and thirdlayers, wherein the third material is identical to the first material,and wherein the third layer has the same thickness as the first layer.6. The component according to claim 1, wherein the electrical connectioncontact comprises at least one contact region for securing theconnection contact on a main body of the ceramic component and at leastone connection region for securing the connection contact on a carrier,wherein the connection region is arranged at an angle with respect tothe contact region.
 7. The component according to claim 1, which isembodied in such a way that, upon the connection contact being securedon a carrier, the main body is spaced apart from the carrier.
 8. Thecomponent according to claim 1, which is embodied as a multilayercapacitor.
 9. A component arrangement comprising a component accordingto claim 1 and a carrier, on which the component is secured.
 10. Thecomponent arrangement according to claim 9, wherein the connectioncontact is connected to the carrier by a connecting material, whereinthe connecting material is a sintering material.
 11. A method forproducing a component according to claim 1, comprising the steps ofproviding the electrical connection contact and the main body of thecomponent, securing the connection contact on the main body.
 12. Themethod according to claim 11, wherein, for securing the connectioncontact, a contact material is applied on the main body and/or theconnection contact, then the connection contact is arranged on the mainbody, and then the contact material is sintered.
 13. A method forproducing an electrical connection contact of a component including amain body having ceramic layers and electrode layers, the electricalconnection contact including a first layer having a first material and asecond layer having a second material arranged thereon, wherein thefirst material has a high electrical conductivity and the secondmaterial has a low coefficient of thermal expansion, wherein theelectrical conductivity of the first material is at least 40 m/Ω mm² andthe coefficient of thermal expansion of the second material is at most 5ppm/K, wherein a relation of the thickness of the second layer to thethickness of the first layer is 1:1 up to 5:1, and wherein theelectrical connection contact is secured on the main body by a contactmaterial, wherein the contact material is a sintering material, themethod comprising the steps of providing a metal sheet comprising thesecond material, rolling the first material onto the second material.